Final answer:
The dielectric in a foil tantalum capacitor is tantalum pentoxide, with the general structure involving a tantalum foil anode and a dielectric layer of tantalum pentoxide, often coupled with a cathode made from materials like manganese dioxide.
Step-by-step explanation:
The material used as the dielectric in a foil tantalum capacitor is tantalum pentoxide (Ta2O5). The general structure of this type of capacitor involves a tantalum foil that acts as the anode, with the tantalum pentoxide serving as the dielectric layer. The cathode is typically made from a material such as manganese dioxide. When manufacturing the capacitor, an electrolytic process is used to grow the tantalum pentoxide dielectric layer on the surface of the tantalum foil. This layer is extremely thin and enables a high capacitance in a small volume. Foil tantalum capacitors are known for their stability and reliability, making them a popular choice for applications where space is at a premium and performance is critical.